For greater convenience and portability many modern electrical devices are designed to be powered by the electric current drawn from dry cells (commonly referred to as "batteries"). For convenience and economy, various rechargeable, or secondary, batteries have been developed for use in such devices. A number of stand alone chargers, separate from the electrical device itself, have been developed for the sole purpose of charging such secondary batteries through, for example, the use of conventional household current. However, due to differences in chemistry, non-rechargeable, or primary, batteries, such as zinc-carbon or manganese dioxide alkaline batteries, may leak, discharge gasses, or in some cases rupture, if subjected to a recharging current. Thus, for safety purposes, stand alone battery chargers are often provided with a means for discriminating between batteries which may be safely recharged therein, and those which may not.
With respect to stand alone battery chargers, there has been suggested different means for discriminating between batteries. Certain known stand alone battery chargers will accept both primary and secondary batteries but will prevent charging accidents by providing the chargers with an electrical circuit capable of distinguishing between batteries which should and should not be charged. Examples of such stand alone battery chargers are disclosed in U.S. Pat. Nos. 4,577,144, and 4,628,243.
Other known stand alone battery chargers are designed to be used with specially manufactured, rechargeable batteries having recharging contacts which are separate and apart from the normal positive and negative battery terminals. The specialized recharging contacts are cooperable only with corresponding charging contacts found in the charger. Thus, while both primary and secondary batteries may be inserted into the charger, only those batteries having the unique recharging contact will be subjected to the charging current. Examples of such stand alone battery chargers are disclosed in U.S. Pat. Nos. 4,489,268, 5,038,093, 5,108,847 and 5,443,924.
Still other known stand alone battery chargers are designed to accept only batteries provided with unique predetermined physical features, such as specialized cathode or anode terminals, whereby the battery charger is able to discriminate between batteries that should and should not be charged. Specifically, these battery chargers are designed to prevent the insertion therein of non-rechargeable batteries which lack the required physical attribute. Examples of such stand alone battery chargers are disclosed in U.S. Pat. Nos. 4,816,735 and 5,057,761 as well as copending U.S. application Ser. No. 08/278,505 entitled "DISCRIMINATING BATTERY CHARGING SYSTEM" by Spellman et al.
To further ease in the portability of electrical devices, many such devices are now designed with integral, rechargeable battery systems having dedicated, secondary batteries incorporated therein. Still other electrical devices have been designed with rechargeable battery systems capable of using either primary or secondary batteries as a source of power and, for the safety reasons previously discussed, are further provided with the ability to prevent the inadvertent charging of primary batteries should such batteries be utilized therein. Specific examples of such systems are disclosed in U.S. Pat. Nos. 4,147,838, 4,602,202, and 4,645,996. However, these known rechargeable battery systems have been found to be lacking from the combined standpoints of safety, cost, manufacturability, and ease of use.
Specifically, rechargeable battery systems currently in use in electrical devices are limited to systems designed solely for use in conjunction with batteries having separate charging contacts. These systems are undesirable due to the high cost of developing and manufacturing both the system and the batteries therefor. Therefore, a need exists for an electrical device having a rechargeable battery system capable of discriminating on a low cost basis between batteries that may be charged, and primary and/or secondary batteries that should not be charged.
What is also needed is an electrical device having a rechargeable battery system that is easy to use and consumer friendly. For example, it is desirous to provide an electrical device into which the consumer may simply place a battery without having to worry about the alignment of recharging contacts with corresponding charging contacts found in the rechargeable battery system.
As a result of these existing needs, it is an object of the present invention to provide an electrical device having a rechargeable battery system that will accept all batteries for use in powering the electrical device while allowing recharging current to be supplied only to batteries having a predimensioned or otherwise predetermined physical feature.
It is yet another object of the present invention to provide an electrical device having a rechargeable battery system that is simple to use and consumer friendly.
It is still another object of the present invention to provide an electrical device having a rechargeable battery system and batteries for use therein that are both simple and inexpensive to manufacture.
It is a further object of the present invention to provide an electrical device having an improved rechargeable battery system where the rechargeable battery system may be designed to be integral with the electrical device or separable therefrom, i.e. as a battery pack.
Other objects and advantages of the invention will become apparent from the detailed description which follows.